RE: [Visualpython-users] rate() function

[Gary S. <st...@nm...>]

> These two numbers can be entirely different.  Your program measures the
> second, which is also what rate() controls.  There is no way to change
> the rendering frame rate in VPython (except to buy a faster computer :),

Question: if you've re-computed a (or requested a new) frame before the
previous one was done rendering, does the rendering re-start with the new
frame? I presume they don't pile up in a buffer somewhere ... 

> Now, what rate() does is fairly simple.  It could be written in Python
(snip)
>   while (delay - (time.time() - origin) > 0):
>       pass
>   origin = time.time()
(snip)
>
> The reason this can still have an effect when your "loop rate" is less
> than N, because your loop will not execute in exactly the same wall
> clock time each time, and rate() does not attempt to average across
> iterations.
> 
> For example, let's say N = 50, and your loop (without the call to
> rate()) takes 10ms for every even iteration and 30ms for every odd
> iteration.  On each even iteration, rate() will sleep for 10ms, so that
> that iteration takes 20ms.  On odd iterations it will not sleep at all.
> The net effect is that the frame rate changes from 50 (20ms average) to
> 40 (25ms average).

Interestingly, replacing the rate() call in my previous program with a
spin-loop of the short you mentioned above (but based on time.clock(),
which on Windows is supposed to be accurate down to microseconds), I still
get the stair-stepping ... which I don't understand. I believe the above
explanation will, at most, provide only a single plateau. Or perhaps I
misunderstood something ...

Gary
strang-@at@-nmr.mgh.harvard.edu